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form 01 carbonate (56 parts of CaO correspond with 100 parts of CaC03).
This furnishes a control of the estimation of the carbonates according to i,
provided always that the magnesia is small in amount; where the magnesia
is not negligible, it must be determined separately, as stated under 4.

6. Removal of the Hardness.—To obtain an indication of the quan-
tities of lime and sodium carbonate to be added to a water to counteract
excessive hardness (see p. 12), the following tests may be made :

Clear lime water is prepared and its content of CaO established by means
of N/5-HC1 in presence of phenolphthalein (i c.c. N/5-HC1 = 0-0056
gram CaO).

To 200 c.c. of the water a few drops of phenolphthalein are added and
the standard lime water run in until a red coloration lasting for some
instants is formed. From the number of c.c. of lime water used, the amount
of lime (CaO) necessary for i litre of the water is calculated.

The turbid liquid from the preceding test is filtered and the filtrate
treated with a slight excess of N/5-sodium carbonate solution ; after a
second filtration, the excess of sodium carbonate in the filtrate is titrated
with N/5-hydrochloric acid (indicator : methyl orange). From the differ-
ence between the number of c.c. of sodium carbonate added and the number
of c.c. of hydrochloric acid necessary to neutralise the excess of this
carbonate, the amount of sodium carbonate which should be added to the
water (as well as lime water) to decompose the calcium sulphate may be
calculated, i c.c. of N/5-sodium carbonate solution corresponding with
0-0286 gram of Na2C03 + 10 H20.

If it is desired to eliminate the sulphates by means of barium chloride,
I part of S03 will require 3-25 parts of commercial, crystallised barium
chloride (assuming an average of 80 % of BaCl2).

* *

Water for steam boilers should be clear and soft and should not contain too
large a proportion of substances which produce incrustations (calcium and
magnesium carbonates, gypsum, silica, aluminium, iron) or corrosion (chlorides,
nitrates). Boiler water softened by the above methods should be only faintly
alkaline (100 c.c. should not require more than 1-1-5 c-c- °f decinormal acid
for neutralisation) and its hardness should not exceed 3-4 degrees, while with
ammonium oxalate it should turn only slightly milky after 1-2 minutes.

Water for washing silk should be of low hardness (this is neutralised with a
small amount of acetic acid) and should contain no iron and little organic matter,

Water for washing starch should be clear, with little organic matter or fixed
residue and free from ammonia, nitrites, nitrates and iron.

Water for sugar factories should be pure, of low hardness and free from alkali
salts—which, impede the crystallisation of the sugar—and from organic matter
and its decomposition products (nitrites, nitrates and ammonia).

Water for brewing or distilling should be clear, odourless, tasteless and neutral;
it should have a medium hardness and contain moderate proportions of calcium
and magnesium salts and of sulphates ; it should contain little chloride or iron
and should be as free as possible from organic matter, nitrites, nitrates, ammonia
and micro-organisms.

Water for dyeworhs should exhibit different characters according to the nature
of the dyeing; in general it should be very pure and have very little hardness
and, especially for delicate colours, should not contain iron.                                                                       l.2o